1. Field of the Invention
This invention relates to new supported olefin polymerization catalyst systems, methods of producing the catalysts and processess of polymerizing and copolymerizing alpha-olefins. More particularly, this invention relates to the preparation of catalyst compositions comprising a metallocene compound, a magnesium containing compound and a polymeric material.
2. Description of the Prior Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
The field of olefin polymerization catalysis has witnessed many remarkable discoveries during the last 50 years. In particular, two broad areas of invention have emerged: first, the discovery of Ziegler-Natta catalysts in the 1950's, which are still being used extensively in the polyolefin industry; second and more recently, the discovery of the highly active metallocene-based catalysts. Since these discoveries, ongoing research has been conducted to improve the performance of the catalysts.
Despite progress in these areas, the catalysts previously known in the art still have limitations. For example, conventional Ziegler-Natta catalysts often display limited activity, which is reflected in high catalyst residues. On the other hand, the metallocene-based catalysts intrinsically posses high activity, although the catalyst precursors and in particularly the cocatalysts required for polymerization, such as aluminoxanes or borane compounds, are very expensive. Another limitation that both systems share is the lengthy method of preparation.
Traditionally, the active components of both Ziegler-Natta and metallocene catalysts are supported on inert carriers to improve and control the product morphology in olefin polymerization. Magnesium chloride and silica have predominantly been used for the preparation of supported olefin polymerization catalysts.
U.S. Pat. No. 4,173,547 describes preparing a supported catalyst for olefin polymerization by treating silica with both an organoaluminum and an organomagnesium compound. The treated support is then contacted with a titanium tetrachloride.
However, procedures typically used for the preparation of suitable magnesium chloride and silica supports, such as spray drying or recrystallization processes, are complicated and expensive. Hence, methods of catalyst preparation previously described have the inconvenience of being complicated and expensive, and these methods do not allow consistency of particle size and particle size distribution. Also, despite the extensive and increasing use of supports for olefin polymerization catalysts, the previously used support materials themselves have several deficiencies. For example, in the case of silica, high calcination temperatures are required to remove water which is a common catalyst poison. This represents a significant proportion of the preparation time of the catalyst. Furthermore, in addition to the calcination treatment of silica, silica supported metallocene catalyst preparations typically require chemical treatment, namely the use of expensive aluminoxane or borane compounds in catalyst preparation
U.S. Pat. Nos. 5,625,015 and 5,595,950 describe a catalyst system in which silica is contacted with an aluminoxane prior to the deposition of the metallocene component.
U.S. Pat. No. 5,624,878 describes direct coordination of a Lewis basic silica to B(C6F5)3 in the presence of an amine reagent. In addition to the expense associated with the aluminoxane or borane, this catalyst preparation procedure itself is complicated and expensive.
The use of silica or magnesium chloride as a support also results in support material largely remaining in the product, which can affect the product properties, such as optical properties, or processing.
One of the objectives of the present invention is to provide a catalyst which overcomes the difficulties encountered in the prior art.